Rearrange file structure

hosts/darwin/system-default.nix

@@ -0,0 +1,54 @@
+{ config, pkgs, nix-homebrew, ... }:
+
+{
+  imports = [
+    ../../modules/homebrew.nix
+    nix-homebrew.darwinModules.nix-homebrew
+  ];
+
+  # Nix configuration
+  nix.settings.experimental-features = "nix-command flakes";
+  nix.settings.substituters = [
+    "https://cache.nixos.org/"
+    "https://nix-community.cachix.org"
+    "https://devenv.cachix.org"
+  ];
+  nix.settings.trusted-public-keys = [
+    "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+    "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+    "devenv.cachix.org-1:w1cLUi8dv3hnoSPGAuibQv+f9TZLr6cv/Hm9XgU50cw="
+  ];
+  
+  # System configuration
+  system.stateVersion = 6;
+  nixpkgs.hostPlatform = "aarch64-darwin";
+  programs.zsh.enable = true;
+
+  # Set primary user for system preferences
+  system.primaryUser = "yanlin";
+  
+  # Security configuration - passwordless sudo for yanlin
+  security.sudo.extraConfig = ''
+    yanlin ALL=(ALL) NOPASSWD: ALL
+  '';
+  
+  # Menu bar spacing configuration using activation scripts
+  # Uses sudo to run as user since activation now runs as root
+  # NSStatusItemSpacing controls horizontal spacing between menu bar items
+  # NSStatusItemSelectionPadding controls padding inside selection overlay
+  system.activationScripts.extraActivation.text = ''
+    echo "Setting menu bar spacing preferences..."
+    sudo -u yanlin defaults -currentHost write -globalDomain NSStatusItemSpacing -int 10
+    sudo -u yanlin defaults -currentHost write -globalDomain NSStatusItemSelectionPadding -int 5
+    
+    echo "Disabling Spotlight indexing..."
+    # Disable Spotlight indexing for all volumes
+    # WARNING: This will break Mail.app search, Time Machine, and other features
+    # To re-enable: sudo mdutil -a -i on
+    sudo mdutil -a -i off
+    
+    # Erase existing Spotlight index to free up disk space
+    echo "Erasing existing Spotlight index..."
+    sudo mdutil -E /
+  '';
+}